Asthma May Effect Fertility

that it look longer for asthmatics to get pregnant (whether or not they were allergic)

Untreated asthmatics took longer to become pregnant than treated asthmatics (including those on inhaled steroids)

How could asthma affect fertility?
Asthma is not just a disease of the lungs, there are systemic features (including higher levels of allergic cells, known as eosinophils, in the blood)

In summary:
Both treated and untreated asthmatics appear at higher risk for subfertility (taking more than 1 year to become pregnant). Is that simply a marker for asthma severity? It is not clear but one thing is certain: taking care of asthma is very important during a pregnancy so in anticipation of that, asthma care should be started and optimized.